Wireless power transfer and charging are emerging technologies for consumer electronic devices, such as smart phones, smart watches, etc. A current trend of development in wireless power technology is to increase the transfer power such that the smart devices can be charged more quickly. However, there are some major limitations for delivering more power wirelessly, such as heat dissipation in the mobile device and electromagnetic interference (EMI) radiation emitted by the wireless power receiver coil. Given these limitations, current devices are not able to produce a wireless charging solution beyond about 10 Watts.
To reduce the thermal loss, down-converting circuitry can be added to the receiver to lower the receiver coil current. A down converter can reduce the voltage from the output of the rectifier while boosting the current presented to the battery charger of a wireless charging system. This conversion allows the same power to be delivered to the receiver while at the same time, reducing the thermal dissipation or loss from the coil into the rest of the device. However, the added down converter raises the impedance presented to the power conversion stages, which in turn lowers the system's quality factor (Q) and increases the system's EMI radiation emissions from the receiver coil. Accordingly, it would be valuable to have a wireless power transfer receiver that reduces heat dissipation and EMI radiation simultaneously.